This invention relates generally to a low pressure mercury vapor discharge lamp of the fluorescent type having a particular type phosphor coating to emit skin tanning radiation when excited by the ultraviolet radiation generated from the mercury vapor discharge. More particularly, the present type lamp construction provides satisfactory skin tanning with a preselected amount of radiation in the approximate 280-320 nanometer ultraviolet region of the spectrum. The ultraviolet radiation in this region is termed UVB radiation and can produce reddening of the skin (erythema) from excessive lamp exposure such as can occur from overexposure to natural sunlight.
Lamps of the fluorescent type to produce artificial skin tanning have been known for some time. The available lamps of this type utilize a coating of a single phosphor material to emit ultraviolet radiation in the approximate wavelength region 320-400 nanometers which is commonly referred to as UVA radiation. Said available lamps produce artificial skin tanning without occasioning skin reddening (erythema) to any significant degree as can occur from overexposure to either natural sunlight or to other types of tanning lamps.
In the United States, the American Conference of Governmental Industrial Hygienists (ACGIH) has established "threshold limit" values for ultraviolet exposure in the workplace. These values are used as guides for those conditions under which it is believed that nearly all workers may be repeatedly exposed--for a nominal eight hours per day--without incurring an adverse effect to the eyes or skin. For the spectral region of the UVA (320-400 nanometers), which constitutes about 97-99% of the ultraviolet radiation emitted, the recommended irradiance or intensity limit on the eyes and skin for the full eight hours is 1,000 microwatts per square centimeter. For the spectral region in the UVC and UVB (200-280 nanometers and 280-320 nanometers, respectively) the radiant exposure upon the unprotected skin and eyes below which a threshold erythema would occur, is 3,000 microwatt seconds per square centimeter weighted in relation to its action spectrum for this effect.
It is further known, however, that UVB radiation is beneficial in promoting efficient skin tanning through formation of melanin pigment which is said to initiate the tanning process. While the exact nature of said beneficial effect is not fully understood at this time, it is known that persons already having melanin pigment present in the skin can tan effectively with UVA radiation alone. It follows from said knowledge that a skin tanning fluorescent lamp which generates both UVA and UVB radiation could thereby promote more effective artificial skin tanning in a sufficient quantity to initiate melanin production. In providing such a lamp, however, there is understandable further need to adhere to the above recommended exposure guidelines so that undesirable erythemal effects are not occasioned.
It is an important object of the present invention, therefore, to provide an improved skin tanning fluorescent lamp which generates both UVA and UVB radiation at a level which enhances artificial skin tanning while minimizing the undesirable erythemal effects.
It is still another important object of the invention to provide an improved skin tanning fluorescent lamp which achieves the desired objectives simply through modification of the coating which produces the desired source of ultraviolet radiation.
These and other important objects of the present invention together with advantages thereof may best be understood by reference to the detailed description which follows taken in connection with the included drawings.